org.jgrapht.alg.shortestpath

Class FloydWarshallShortestPaths<V,E>

java.lang.Object

org.jgrapht.alg.shortestpath.FloydWarshallShortestPaths<V,E>

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

ShortestPathAlgorithm<V,E>

public class FloydWarshallShortestPaths<V,E>
extends java.lang.Object

The Floyd-Warshall algorithm.

The Floyd-Warshall algorithm finds all shortest paths (all n^2 of them) in O(n^3) time. It can also calculate the graph diameter. Note that during construction time, no computations are performed! All computations are performed the first time one of the member methods of this class is invoked. The results are stored, so all subsequent calls to the same method are computationally efficient.

Nested Class Summary

Nested classes/interfaces inherited from interface org.jgrapht.alg.interfaces.ShortestPathAlgorithm

ShortestPathAlgorithm.SingleSourcePaths<V,E>

Constructor Summary

Constructors

Constructor and Description
FloydWarshallShortestPaths(Graph<V,E> graph) Create a new instance of the Floyd-Warshall all-pairs shortest path algorithm.

Method Summary

Modifier and Type	Method and Description
double	getDiameter() Compute the diameter of the graph.
V	getFirstHop(V a, V b) Returns the first hop, i.e., the second node on the shortest path from a to b.
V	getLastHop(V a, V b) Returns the last hop, i.e., the second to last node on the shortest path from a to b.
GraphPath<V,E>	getPath(V a, V b) Get a shortest path from a source vertex to a sink vertex.
ShortestPathAlgorithm.SingleSourcePaths<V,E>	getPaths(V source) Compute all shortest paths starting from a single source vertex.
double	getPathWeight(V source, V sink) Get the weight of the shortest path from a source vertex to a sink vertex.
int	getShortestPathsCount() Get the total number of shortest paths.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FloydWarshallShortestPaths

public FloydWarshallShortestPaths(Graph<V,E> graph)

Create a new instance of the Floyd-Warshall all-pairs shortest path algorithm.

Parameters:

graph - the input graph

Method Detail

getShortestPathsCount

public int getShortestPathsCount()

Get the total number of shortest paths. Does not count the paths from a vertex to itself.

Returns:

total number of shortest paths

getDiameter

public double getDiameter()

Compute the diameter of the graph.

Returns:

the diameter (longest of all the shortest paths) computed for the graph. If the graph contains no vertices, return Double.NaN. If there is no path between any two vertices, return Double.POSITIVE_INFINITY.

getPath

public GraphPath<V,E> getPath(V a,
                              V b)

Get a shortest path from a source vertex to a sink vertex.

Parameters:

a - the source vertex

b - the target vertex

Returns:

a shortest path or null if no path exists

getPathWeight

public double getPathWeight(V source,
                            V sink)

Get the weight of the shortest path from a source vertex to a sink vertex. Returns Double.POSITIVE_INFINITY if no path exists.

Specified by:

getPathWeight in interface ShortestPathAlgorithm<V,E>

Parameters:

source - the source vertex

sink - the sink vertex

Returns:

the weight of the shortest path from a source vertex to a sink vertex, or Double.POSITIVE_INFINITY if no path exists

getPaths

public ShortestPathAlgorithm.SingleSourcePaths<V,E> getPaths(V source)

Compute all shortest paths starting from a single source vertex.

Specified by:

getPaths in interface ShortestPathAlgorithm<V,E>

Parameters:

source - the source vertex

Returns:

the shortest paths

getFirstHop

public V getFirstHop(V a,
                     V b)

Returns the first hop, i.e., the second node on the shortest path from a to b. Lookup time is O(1). If the shortest path from a to b is a,c,d,e,b, this method returns c. If the next invocation would query the first hop on the shortest path from c to b, vertex d would be returned, etc. This method is computationally cheaper than calling getPath(Object, Object) and then reading the first vertex.

Parameters:

a - source vertex

b - target vertex

Returns:

next hop on the shortest path from a to b, or null when there exists no path from a to b.

getLastHop

public V getLastHop(V a,
                    V b)

Returns the last hop, i.e., the second to last node on the shortest path from a to b. Lookup time is O(1). If the shortest path from a to b is a,c,d,e,b, this method returns e. If the next invocation would query the next hop on the shortest path from c to e, vertex d would be returned, etc. This method is computationally cheaper than calling getPath(Object, Object) and then reading the vertex. The first invocation of this method populates a last hop matrix.

Parameters:

a - source vertex

b - target vertex

Returns:

last hop on the shortest path from a to b, or null when there exists no path from a to b.